The present invention relates to an improvement in an electrostatic recording apparatus which includes a photoconductive element and devices for implementing a charging, exposing, developing, transferring, fixing and other various functions, e.g. a copier, a facsimile apparatus or a printer.
A prior art electrostatic recording apparatus of the kind described has various problems left unsolved, as enumerated below.
(1) Generally, in an electrostatic recording apparatus, a latent image electrostatically formed on a photoconductive element is developed by toner which is conveyed by a developing roller. In order that an even high-quality toner image may be produced, the developing roller has to be maintained at a constant spacing from a photoconductive element. In practice, however, the developing roller is apt to move toward the photoconductive element or to oscillate, disturbing the toner image to cause so-called jitter and others. Especially, in the case than a developing device is bodily detachable relative to the photoconductive element, the tendency of the developing roller to oscillate is pronounced since the ease of attaching and detaching is preferred in such a case.
(2) In a developing system in which a photoconductive element and a developing roller are held in contact, i.e., a contact developing system, carrier and, therefore, the replacement of carrier is needless and, yet, non-magnetic toner having good fixing property is usable. Another advantage attainable with such a system is that a toner image produced appears with a sharp contour. A prerequisite with this system is maintaining a predetermined contact pressure between the photoconductive element and the developing roller. However, because the developing roller is driven by a gearing which uses a drive gear, a force which tends to thrust the developing roller aside is imparted from the drive gear to the developing roller as the load acting on the developing roller increases with the elapse of time. Such a force would increase the contact pressure to an unusual degree, thereby, lower the image quality.
(3) In an electrostatic recording apparatus of the type described, a photoconductive element, feed rollers and others are individually driven by a servo motor which is controlled to rotate at a constant speed. The constant speed control over the servo motor needs a servo circuit and other constant-speed control means. It has been customary to provide a driver stage, which includes the constant-speed control means, on a circuit board having a CPU (central processing unit) and other control circuits and independently of the servo motor, the driver stage being connected to the servo motor by a long cable. This kind of connection is disadvantageous in that an extra space for wiring is necessary which obstructs miniaturization of the recording apparatus and in that noise is apt to be picked up.
(4) In the event of inspection and repair of such an electrostatic recording apparatus, e.g., when a sheet has jammed the apparatus, it is often needed to bare an exposing unit, developing unit and others of the apparatus to facilitate serviceman's or operator's access. Such has heretofore been implemented by removing the front panel, top cover or the like of the apparatus. However, this kind of implementation cannot achieve sufficient exposure of the various units, forcing troublesome labor on the serviceman or the like.
(5) Electrostatic recording apparatuses of the kind described include a one which has a capability of detecting jams of transfer materials on a sheet transfer path. Specifically, the jam detection is such that a period of time which a transfer material of B4, A4 or like regular format takes to move past a certain point of a transport path is counted and, when the transfer material has moved past that particular point within a predetermined period of time, it is decided that a jam has not occurred while, when it has failed to do so, it is decided that a jam has occurred. A problem with such an apparatus with a jam detection capability is that the printing process cannot be effected smoothly unless the transfer material is of a regular format, i.e., an envelope or like transfer material which is irregular in size prevents the jam detection capability from being correctly executed.
(6) There is also available an electronic recording apparatus of the type having an upper and a lower unit each accommodating various devices. In this type of apparatus, the upper unit is rotatable away from the lower unit to facilitate maintenance removal of a jamming sheet, and others. When the upper unit is raised, the interior of the apparatus is exposed to the outside. Since continuing the operations of the various devices under such a bare condition is dangerous, an interlock switch is turned off in response to the upward movement of the upper unit so as to deactivate the devices. However, should the interlock switch be left exposed, a person might accidentally touch it to get into danger.
(7) In an electrostatic recording apparatus having an upper and lower unit as stated above, the two units are connected together and locked before an actual printing operation is started. A prior art device for locking the two units is implemented with pawls, hooks, knobs and others which are mounted on the units. This, however, adds to the number of parts required while rendering the production troublesome.
(8) In an electrostatic recording apparatus, various devices are usually housed in a casing so that data may be recorded by those devices on a transfer material which is fed along a predetermined transport path. Customarily, the transport path has been implemented with an exclusive rib member which is secured to the casing. The rib member, however, increase the numbers of parts as well as the number of production steps and, thereby, the cost.
(9) A paper sheet to which a toner image has been transferred by a transfer step of a series of electrophotographic process may be heated by a heat type fixing device, as well known in the art. A problem with a heat type fixing device is that it not only heats itself to an extremely high temperature but also adversely affects various nearby devices. Especially, in a recording apparatus of the type having a waste toner tank in the vicinity of such a fixing device, waste toner stored in the tank melts and adheres due to the heat.
(10) Generally, a fixing device of the kind described is controlled in temperature by use of a thermistor. So long as the transfer material used is of a comparatively large size, the position where the thermistor is disposed is not critical. However, in the case of a transfer material whose size is relatively small, should a transport path for the transfer material and the thermistor be spaced a substantial distance from each other, temperature cannot be accurately controlled in relation to the transfer material. Especially, when a pasted envelope is fed as a small-size transfer material, accurate temperature control is desired for preventing paste from melting.
(11) In an electrostatic recording apparatus of the type described, the surface of a photoconductive element is uniformly charged by the discharge of a charger before exposed imagewise. The discharge is accompanied with generation of ozone. Ozone surrounding the photoconductive element would aggravate deterioration of the photoconductive element and, in the event of maintenance, cause a serviceman to feel uneasy.
(12) An electrostatic recording apparatus of the type described includes a transfer charger which transfers a toner image from a photoconductive element to a transfer material. By such a transferring step, the transfer material is caused to electrostatically adhere to the photoconductive element. To separate the transfer material from the photoconductive element, use may be made of a pawl, as well known in the art. On the other hand, the charge on the photoconductive element is dissipated after the image transfer so as to remove remaining toner. Heretofore, the separation of a transfer material by the pawl and the charge dissipation from the photoconductive element has been performed independently of each other by exclusive devices. Such is undesirable from the space and cost standpoints.
(13) Further, there is available an electrostatic recording apparatus in which a photoconductive element and other various devices are detachably mounted on the housing of the apparatus for facilitating replacement of those elements which failed or wore out. Specifically, the structure is such that the devices are simply put in individual mounting positions of the housing. This brings about a problem that a serviceman has to start a recording operation with an uneasy conscience, i.e., without knowing if each device has been surely mounted.